1. Field of the Invention
The present invention relates to a gas-fired water heater, comprising an upright thermally insulated cylindrical water tank, a central exhaust flue extending axially through the water tank and a combustion chamber arranged under the exhaust flue, which has an atmospheric gas burner in it. The atmospheric gas burner has a flat burner mat and a complete pre-mixing gas/air supply system with a combustion-gas-single-barreled combustion gas nozzle, which has an intake for the combustion gas and combustion air arranged outside of the combustion chamber.
2. Description of the Related Art
Gas-fired water heaters are marketed in many different embodiments for different applications. They serve especially for supplying hot water in homes or houses. The so-called boiler for supplying hot water is a typical unit of this sort.
The present invention relates to a special, gas-fired water heater, the so-called “water heater”, as is typically extensively used in households, work places and small industrial plants, as a free-standing hot water reservoir for hot water supply, for example, for taking showers.
This “water heater” has a typical structure, as described for example in U.S. Pat. No. A 4,953,510. The central component of the water heater is a longitudinally extending cylindrical reservoir tank for storing the heated water, through which a central exhaust flue extends and which is free-standing on the ground or floor by means of feet.
An open atmospheric gas burner with suitable power is arranged under the reservoir tank, whose lower wall is cup-shaped. This atmospheric gas burner causes hot exhaust gas including combustion products to rise and flow against the bottom of the water tank and subsequently through the long exhaust gas flue. In this type of water heater the hot gas flowing upward in the exhaust gas flue contacts the inner surfaces of the flue pipe, while the water in the reservoir tank is in contact with the outer surfaces of the flue pipe. During the combustion process the water inside the reservoir tank is heated by heat conduction through the wall of the exhaust flue. In this type of water heater normally a long separating wall is arranged within the exhaust gas pipe in order to improve the efficiency of the heat transfer from the hot combustion gases through the wall of the exhaust flue to the water within the reservoir tank. Furthermore this sort of water heater can have a thermally activated valve, which halts combustion by the gas burner, when the temperature of the water inside the reservoir reaches a predetermined temperature. In order to reduce the heat losses from the water heater during heating of the water and also after halting the combustion process, the exterior surfaces of the reservoir tank are typically covered with a heat insulating material.
There has been increasing strengthening of legislation regarding avoiding accidents, caused when inflammable vapors rise into the open combustion region, and increasing improvements in exhaust gas evaluation. This has led to development of water heaters a, which do not have an open combustion arrangement but instead have a closed combustion chamber, in which a completely pre-mixing gas burner, a so-called pre-mix burner, is arranged.
This sort of water heater is described in U.S. Pat. No. 5,875,739. The structure and arrangement of the pre-mix burner in the closed combustion chamber is shown in FIG. 3 of the present application, which is taken from the aforementioned U.S. Patent. This cross-sectional view shows a water heater with a water tank 1 and a closed combustion chamber 2, to which an exhaust flue 3 is connected, which extends centrally through the water tank 1. Combustion chamber 2 and water tank 1 are thermally insulated from the surroundings by thermal insulation 4. An atmospheric pre-mix burner 5 is arranged in the combustion chamber 2. The atmospheric pre-mix burner comprises a mixing chamber 6 and a spherical combustion surface 7. A Venturi-pipe 8 is connected to the mixing chamber 6, which extends through the thermal insulation 4 to the outer surfaces of the water heater. A gas nozzle 10 for supplying combustion gas is arranged within the outer opening 9 of the Venturi-pipe 8. When combustion gas flows into the Venturi-pipe 8 through the gas nozzle 10, primary air is drawn in through the outer opening 9 because of the flow action properties of this pipe, which is then mixed with the combustion gas by turbulence in the mixing chamber 6.
Another embodiment of a water heater with a complete pre-mixing atmospheric gas burner is described in U.S. Published Patent Application U.S. 2003/0111 023 A1. The gas burner 5 described in this reference has a plane rectangular burner mat 7, as shown in FIG. 4 of the present application, which is taken from the aforementioned U.S. Patent Application. This figure shows the mixing chamber 6 with the molded Venturi-pipe 8 including the feed 10 of combustion gas and the feeds 9 of primary air.
In both references water heaters with combustion chambers, which are completely sealed and kept at low pressure, without a powered mechanical blower or fan, are described. Intake of additional combustion air, also called secondary air, is not possible and undesirable in regard to maintaining exhaust gas quality, because the combustion chamber is sealed from the surroundings. If additional combustion air could flow in, the required low values of CO and NOx concentration could not be attained. However sealing the combustion chamber from the surrounding air is only accomplished with extra effort and is not economical.
The closed, completely sealed combustion chamber makes servicing and maintenance, and also construction, of the gas burner difficult. The comparatively heavy reservoir tank must be separated from the combustion chamber in order to gain access to the gas burner in the combustion chamber, which is possible only with the help of a block and tackle or hoist or some other lifting tool. Also the combustion chamber must be tightly sealed again during re-assembly.